1. Field of the Invention
The present invention relates to a foam type fire extinguishing agent for hydrophylic combustible liquids. More particularly, the present invention relates to a fire extinguishing agent which exhibits high foaming ability upon dilution with not only fresh water but also sea water, which generates foams having excellent alcohol resistance and flowability and which can effectively extinguish fires of hydrophilic combustible liquids. Further, the fire extinguishing agent of the present invention possesses various characteristics in addition to those described above, such as about a neutral pH, low viscosity, a low solidifying point (-5.degree. C. or below), largely reduced deterioration under prolonged preservation, and which is effective in extinguishing fires of hydrophilic combustible liquids even when used in dilutions of 3%.
2. Description of Prior Art
In general, when most foam type fire extinguishing agents, which have commonly been used for extinguishing fires of petroleum, are employed for extinguishing fires of so-called hydrophilic combustible liquids such as alcohols, ketones, ethers, esters and the like, no sooner does the foam generated by such fire extinguishing agents contact the burning surfaces than it melts away. Thus it is impossible to cover the burning surface with the foam and it is not possible to extinguish the fire.
Many foam type fire extinguishing agents useful for extinguishing fires of hydrophilic combustible liquids have been proposed, and they can generally be classified into the following three groups:
(1) Fire extinguishing agents of the type which contain decomposition products of natural proteins as a base material and contain metal soaps dispersed in the base material with the aid of triethanolamine or the like.
(2) Fire extinguishing agents in which metal soaps are solubilized and dispersed in synthetic surface active agents.
(3) Fire extinguishing agents which contain water soluble high polymers in large amounts and further contain surface active agents of the fluorinated aliphatic system and other foaming agents.
Fire extinguishing agents of the first group (1) are prepared by solubilizing and dispersing large quantities of water insoluble metal soaps into fire extinguishing agents with the aid of amines or the like, and stock solutions of such agents rarely have pH values around neutrality. Therefore, they are accompanied by several disadvantages. For example, containers therefor are subject to corrosion, the chemicals are dangerous to the human body, and deterioration such as precipitation and separation are likely to occur during prolonged storage. In addition, they lose their fire extinguishing ability through precipitation of the metal soaps from water solutions if they are not foamed immediately after mixing with water.
The foam generated by fire extinguishing agents of group (1) is excellent in so-called alcohol resistance (i.e., the foam does not melt upon contact with alcohols), but the generated foam is very hard and caky. Under such circumstances, the agent frequently fails because the foam cannot flow and spread over the entire burning area. Moreover dilution with sea water causes a remarkable drop in the foaming ability. Further, fire extinguishing agents of the group (1) are far from being economical because they have been made available for practical use in only 6% dilutions (The term "dilutions" is used throughout this specification in the manner in which it is used in this art. A 6% dilution is a dilution of 6 parts by volume foam liquid with 94 parts by volume water.).
On the other hand, extinguishing agents of the second group (2) possess low foaming abilities, and the alcohol resistance of the generated foam is low. Though they are on the market in a 3% dilution, large quantities of agents are required to achieve fire extinguishing because the fires cannot be put out until the burning liquids are considerably diluted by casting a large quantity of foam thereinto. Moreover, the fire extinguishing effect cannot be accomplished in case of liquids such as butanol for which the dilution effect is not so great, and in the case of liquids such as acetone which have a strong calorific force and a strong defoaming action.
The agents of the third group (3) are characterized by the addition of water soluble high polymers having high hydrating abilities, and the solutions of such water soluble high polymers cause syneresis in hydrophilic combustible liquids to result in the formation of gelatinous mat, and thereby the foam existing thereon can be protected. Fire extinguishing agents of this type are supposed to exhibit higher extinguishing power because the foam generated from them has better spreadability than the foam generated from the fire extinguishing agents of group (1). However, frequently the gelatinous mat formed inhibits the spreadability of the foam. In addition, viscosities of stock solutions of fire extinguishing agents are very high due to the addition of large quantities of water soluble high polymers. Further, the need for comparatively high concentrations of high polymers contained in water solutions (gelatinous mat cannot be formed when the concentrations of high polymers in water solutions are too low) makes it necessary to employ dilution ratios of 6% or higher in practice. Due to the high viscosity (on the order of 1000 cs or above) inherent in the stock solution of the fire extinguishing agent of the third type, bubbles arise in the course of preparation or charging, or a great change in viscosity is caused by variation in surrounding temperature. Furthermore storage of such a stock solution in a cold place is difficult due to the high solidifying point of the agent which is in the vicinity of 0.degree. C. As described above, the fire extinguishing agents of the third type have various disadvantages. Moreover, they are very expensive though those which contain as additives fluorinated aliphatic surface active agents are on the market.
The problems which occur when conventional fire extinguishing agents are employed for fires of combustible liquids other than petroleums are summarized below:
One problem related to stock solutions of the agents in which a metal soap is dispersed in the decomposition products of natural proteins is that they are not only unstable in themselves but also attended by unavoidable precipitation of metal soaps when diluted with water at the time of practice, because metal soaps are generally insoluble in water and solvents commonly used for preparations of the stock solutions. In addition, they are also accompanied by a decrease in foaming ability when the stock solutions are diluted with sea water. Another problem related to agents which contain metal soaps dispersed in surface active agents is the inevitable technical limitation that since the addition of metal soaps causes a large drop in the foaming ability, it is necessary to restrict the addition amounts of metal soaps to low levels in order to raise the foaming ability, but if this is done the agents lose larger portions of their alcohol resisting abilities. It is, of course, almost impossible to use these agents diluted with sea water, and physical properties inherent in the stock solutions of such agents, such as solidifying point and the like, are not good and they can be little improved by the addition of large amounts of solvents. A further problem related to agents containing water soluble high polymers is physical properties and resistance to cold weather are so poor that ordinary foaming apparatuses cannot be used in the winter season and in a cold region, and special apparatuses are required to force such agents to foam.